Field of the Disclosure
This disclosure pertains to switching power converters with power factor correction.
Description of the Related Art
Power factor in switching power converters is defined as the ratio of the real power delivered to the load to the apparent power provided by the power source. Utility companies or government agencies require power factors in switching power converters to exceed a certain minimum level by regulation. Thus, switching power converters should deliver power from the power source to the load with a high power factor and low total harmonic distortion (THD).
Current single-phase active power factor control techniques are generally divided into two categories: a two-stage approach and a single-stage approach. In the two-stage approach, a power factor control front-end stage converts alternating current (AC) input voltage into a direct current (DC) voltage on a bulk energy storage capacitor. A DC/DC converter such as a flyback switching power converter is used as the second output stage to provide isolated and regulated low output voltage or high output current to a load. In contrast, the single-stage approach combines the power factor control stage with the DC/DC stage into a single stage. In the single-stage approach, a single switch is controlled to achieve the dual function of input power factor correction and output voltage/current regulation.
Generally, two-stage power factor control circuits utilize a separate stage to shape the input current to be near sinusoidal and in phase with the input line voltage to achieve high input power factor and low THD. However, the efficiency of the two-stage power factor control circuits is generally lower than the single-stage power factor control circuits because energy is processed twice in the two stages of the two-stage power factor control circuits. Furthermore, because of the use of two stages, two-stage power factor control circuits are more complex and costly compared to single-stage power factor control circuits. Thus, single-stage power factor control circuits are usually preferred for low-power applications due to cost and efficiency considerations.